The invention relates to a piston valve for charging and discharging fluid in a fluid chamber. In a preferred embodiment of the invention, the piston valve is used in a high pressure high temperature environment, (HPHT) specifically HPHT press apparatuses. For example, such presses are useful in the superhard materials production industry. Some examples of superhard materials high pressure high temperature presses produce and sinter include cemented ceramics, diamond, polycrystalline diamond, and cubic boron nitride. HPHT press apparatuses typically require significant structural mass to withstand the ultra high pressures essential to synthetically form superhard materials. Various press designs are known in the art of superhard materials production and have employed assorted concepts to contain the immense reaction forces that are required to process superhard materials. For example, U.S. Pat. Nos. 2,918,699 and 3,913,280 disclose a tie-bar frame press design. Generally, the tie bar press relies on press mass largely to prevent press rupture during press cycle in which bending moments of the tie bars become great. In conventional tie-bar press systems, the length and diameter of the piston cylinders are proportional to the overall size of the press, and the hydraulic fluid must be pumped to the press at pressures ca. 10,000 p.s.i. or more which require specially made high-pressure pumps, hoses, and fittings. The high internal pressures of a reaction cell required to produce superhard materials necessitates a large amount of force applied to reaction cell faces. Because the piston cylinders of a tie bar press design generally operate jointly and at the same pressures thus producing the same force on a reaction cell, only equilateral polyhedron type reaction cells are possible.
A modern HPHT press apparatus comprises a unitary frame and six removeable high-pressure cartridges. A cartridge for a prior art unitary frame press apparatus comprises a low-pressure chamber and a high-pressure chamber joined by a cylindrical passageway. A “T” shaped intensifying piston having an axial through bore is disposed in the passageway with its large diameter end in the low-pressure chamber and its small diameter end in the high-pressure chamber. The area differential of the two ends provides the intensification ratio of the piston. A hydraulic fluid manifold encloses the low-pressure chamber, and a main piston encloses the high-pressure chamber. A dagger having an axial through bore and having an outside diameter corresponding to the inside diameter of the piston's axial through bore, is attached to the manifold and inserted through the bore of the intensifying piston. The dagger extends from the manifold through the low-pressure chamber and the cylindrical passageway. The dagger also provides a fluid path between the manifold and the high-pressure chamber. As the piston moves along the dagger path through the passageway and into the high-pressure chamber, it pressurizes the fluid in the high-pressure chamber behind the main piston. By changing the diameter of the intensifying piston's axial through bore, and the corresponding outside diameter of the dagger, the area of the piston's small end is also changed, and the intensification ratio altered. Accordingly, the fluid pressure within the high-pressure chamber may be increased or decreased in order to accommodate a desired application.
The dagger in the prior art apparatus requires the use of high pressure seals and a manifold check valve to control the fluid pressure in the high pressure chamber, which may be over 40,000 psi. In time the seals degrade and the check valve is prone to contamination and failure creating a hazardous condition in the operation of the press.
The prior art presses are often classified by the tonnage of pressure they are capable of exerting on a reaction cell, the container which is inserted into the press reaction chamber that houses the sintering raw material for transformation under high pressures and temperatures into superhard materials. For example, a 3000-ton multi-axis press typically is capable of producing approximately 700,000 psi. on each face of a cubic reaction cell. During the press cycle, the reaction cell is usually subject to ultra high compressive forces and temperatures; the pressure inside the cell must reach 35 kilobars or more to produce superhard materials such as polycrystalline diamond. Simultaneously, an electrical current is passed through the cell's resistance heating mechanism raising the temperature inside the cell to above 1000° C. After the reaction cell is subject to high pressures and temperatures for a set period of time, it is quickly cooled. Pressure is then released on each side of the cell and the cell is removed from the internal reaction chamber.
The amount of compressive forces a high pressure high temperature press can exert on a given reaction cell and consequently the maximum reaction cell size and payload, are limited by the reaction forces the press can endure without catastrophic rupture. Most often, the size and mass of the press determines its threshold capabilities for tonnage before catastrophic rupture occurs. For example, the weight of a tie-bar press with a tonnage rating of 3000 tons may exceed 60 tons. The weight of a 4000-ton tie bar press may exceed 100 tons. Moreover, large tonnage press types as described above are often expensive to construct and its efficiency is typically proportional to the duration of its cycle and volume of its payload. Therefore, in general, the smaller the press mass and the shorter the duration of the pressing cycle, and the larger the reaction cell with concomitant enlarged payload volume, then the higher the economy and efficiency of the multi-axis press. Essentially, the greater reaction forces a press design can withstand at a given mass in conjunction with decreased energy consumption per cycle and increased reaction cell payload, then the manufacture of superhard materials becomes more economically viable.